Dynamic Force Analysis

Kinetostatic approach:

• Also known as inverse dynamics
• Solve for kinematics first
• Calculate forces and torques required to yield the desired motion
• Equations will focus on desired accelerations

Newton’s second law in vector form:

$$\begin{array}{rl}\mathbf{F}& =m\mathbf{a}\\ \mathbf{T}& =I_G\alpha \end{array}$$

Scalar form:

$$\begin{array}{rl}\sum F_x& =m{a}_x\\ \sum F_y& =m{a}_y\\ \sum T& =I_G\alpha \end{array}$$

We will be neglecting the contribution of weight forces ($mg$) for our dynamic force analysis, as it is typically negligible compared to the involved kinematic accelerations. If the mechanism or machine we are considering has a very large mass (and hence weight) or has small kinematic accelerations (i.e., moving slowly), we will need to reconsider this assumption and include weight in your analysis.